A continuing demand exists for a simple, inexpensive radiation shield which can be used to simplify the installation and/or removal of shielding material as may be necessary to achieve reductions in dose exposure to personnel in nuclear power operations, particularly as regards exposure to gamma radiation. This is true today, even though flexible lead shielding, or encased lead shielding has heretofore been widely used for providing certain types of radiation shielding. In fact, in older nuclear power plants, the dose exposures to plant workers due to accumulations of radioactive materials in plant structures, and in particular, pipe runs, increasingly have brought this problem to the attention of plant operational personnel. During maintenance and overhaul of power plant systems, personnel are frequently required to perform operations that bring them into close proximity to locations which have the potential to accumulate, and thus emit, potentially harmful ionizing radiation.
Generally, the prior art apparatus and methods known to me are too cumbersome, and they are not particularly well adapted to being secured in place for long term radiation protection. As a result, the overall radiation dosage received by nuclear plant workers could be appreciably reduced with the availability of improved radiation shielding devices, and in particular, with improved devices that are suitable for being left in place for continued use during long term plant operations.
It would also be desirable for a number of reasons to be able to utilize multiple radiation shield portions in a radiation shield application. First, multiple shield portions could be used to increase the shielding effect, by combining the shielding capability of multiple layers of radiation shield portions. Second, multiple shield portions could be utilized to efficiently accommodate a varying dimensional requirement, such as the curve of a pipe, or an elbow in a pipe run. Third, many fabrication personnel find that it would be desirable to have radiation shield portions which can be conveniently fastened together to produce a final radiation shield of a desired size, in an easy, building block fashion.
One important problem which must also be overcome with respect to any lead based radiation shield design is the potential for contamination of lead by existing radioactively contaminated materials, as that would result in further contamination since the lead may itself become radioactive. In other words, the use of a lead shield necessitates protection of such a lead shield, to avoid the possibility of further contamination, of either the lead itself, or of the underlying area due to lead becoming deposited thereon. This problem is further aggravated when the shields are placed in locations subject to high temperature or to water spray. Depending upon the anticipated service, a radiation shield may be subject to various adverse or harsh operating conditions, and thus the design must accordingly be capable of reliably protecting the lead during such service.
Currently, when it becomes necessary to work on or near pipe runs which are emitting an appreciable radiation dosage, common practice has been to use a type of wool blanket, or lead shot bags, or lead strips. Each of such apparatus and the methods for their use are somewhat effective in reducing radiation dosage, but in each case, their use has certain drawbacks, including:
(1) the equipment is too bulky (especially in the case of a lead wool blanket); PA1 (2) the equipment is prone to leak (such as in the case of lead shot bags, where loss of lead causes other contamination problems); and PA1 (3) installation of the apparatus is too time consuming (such as in the case of installation of lead sheet strips). PA1 can be used in radioactively contaminated areas with minimal risk of contamination by the lead from the shield; PA1 can be provided in a simple coating that allows use in moderately moist environments; PA1 can be used where the shielding is not expected to encounter high temperatures; PA1 can be used where the shielding is not expected to encounter high pressure water spray; PA1 which can be used in direct contact with stainless steel piping and components; PA1 are relatively simple, particularly in the manufacture and installation, to thereby enable the devices to be easily prefabricated and installed for unique applications; and PA1 which can be easily decontaminated. PA1 can be easily used with stainless steel plate as the encapsulating material, so as to allow use in areas which may encounter high pressure spray; PA1 can be used in radioactively contaminated areas with an absolute minimum of risk of contaminating the lead in the shield; PA1 can be used on or around piping and components requiring that the shielding be protected against moisture, heat, and high temperature water or steam; PA1 can be left inside the primary containment building during operation of the nuclear reactor plant. PA1 compatible with direct stainless steel contact; PA1 easy to decontaminate; PA1 able to withstand short duration exposure to water or spray; PA1 able to withstand short duration moist temperatures to about 145.degree. F.; and PA1 are able to withstand moderate flexing and bending, without cracking and peeling. PA1 compatible with use in moderately high temperature environments (up to 450.degree. to 500.degree. F.); PA1 able to withstand prolonged exposure to moisture and high pressure water or steam spray; PA1 are able to withstand moderate flexing and bending; PA1 easy to install and to remove.
Although at least one proprietor has recognized the need for an improved radiation shielding that is available in sizes that can be manipulated by hand by a single workman, and which protects the underlying structure from lead contamination, unfortunately, such devices known to me have left something to be desired. Consequently, I have developed novel radiation shielding designs, and methods for their fabrication, and for their installation, which provide radiation shielding which is superior to earlier radiation shielding apparatus and techniques which are known to me.
Radiation shielding devices which provide some of the general capabilities desired have heretofore been proposed. Those of which I am aware include those described in the following patents: U.S. Pat. No. 5,012,114 issued to Sisson on Apr. 30, 1991 for a Radiation Shield; and U.S. Pat. No. 3,785,925 issued to Jones on Jan. 15, 1974 for a Portable Radiation Shield for Nuclear Reactor Installation.
The patent documents identified in the preceding paragraph disclose devices which do not provide permanently affixable radiation shield designs, and thus are inherently not as well suited, as disclosed, for many of the applications which are of interest to me. The radiation shielding devices provided by Sisson are not suitable for exposure to moderate or high temperatures, or to water spray environments, due to use of a vinyl plastic sheet as a protective surface material. And, the portable shield provided by Jones, which is designed for protection of the dry well during removal of fuel from a BWR plant, though it involves the provision of a lead filled stainless steel shielding device, is so large and unique as to be inapplicable for most of the smaller applications of interest to me. Therefore, there still remains an unmet and increasingly important need in the field for a radiation shield which is designed and manufactured in a way that assures sufficient structural strength to withstand use for either permanent or temporary service in harsh conditions, and which have the assurance that retrieval is possible without encountering adverse lead contamination. Thus, the advantages offered by my novel radiation shield designs, which are permanently mountable (even in highly controlled locations such as a dry well) and which may be provided in sizes which are transportable by a single worker, yet be removable and cleanable, are important and self-evident.